The present invention relates to a heat sensitive copying machine and a heat sensitive sheet for use therewith.
There are various kinds of heat sensitive copying machines. One such heat sensitive copying machine is used to make a transparent original carrying an image such as characters, illustrations and/or drawings to be projected by the use of an overhead projector onto a remote screen. Recent overhead projectors are portable so as to be easily carried around. However, if it is needed to make a transparent original where the overhead projector is used, it is usual that there is no copying machine.
For making it possible to make transparent originals anywhere an overhead projector is used, a portable overhead projector with a heat sensitive copying device built therein has been disclosed in Japanese Patent Appln. No. 62-110,300. With the overhead projector with a built-in heat sensitive copying device mentioned above, it is quite convenient to make and project transparent originals as needed. The overhead projector with a built-in heat sensitive copying device uses a transparent heat sensitive sheet with a recording layer containing particles which are blackened by heat applied by a thermal printing head so as to form thereon the same image as on an original. A copied transparent original is placed with the recording layer side up on a reflecting Fresnel plate of the overhead projector to be projected onto a remote screen.
Such transparent originals are generally apt to curl concavely with the recording layer inside due to the application of radiant heat thereto. When such a curled transparent original is placed on the reflecting Fresnel plate and illuminated from the back by a light for projection, it becomes more curled. This leads a fuzzy or out-of-focus image projected onto the remote screen.
There are sometimes the need to write notes on the transparent original while projecting the same. In such cases, because the transparent original is placed with the recording layer outside, and because there are some compositions of recording layers that do not receive ink, it is hard to write notes on the transparent original. Even if it is possible to write notes on the recording layer of the transparent original, the recording layer can be damaged when the written notes are rubbed out.
Another type of such heat sensitive copying machine is known, in the form of a so-called electronic writing board which is a writing board capable of making a hard copy of notes, illustrations or the like written thereon. One such electronic writing board includes a writing surface such as the writing board itself or a sheet drawn over the writing board from a roll, on which notes, illustrations or the like are written. An image of a selected part of the writing sheet is electrically read by an image sensor such as a CCD sensor and printed out as a hard copy.
Such writing boards with heat sensitive copying machines incorporated are not only difficult to carry around but also incapable of making hard copies of surfaces or materials on the surfaces of usual writing boards. For solving this problem, an apparatus for copying a surface of a writing board is disclosed in, for example, Japanese Patent Unexam. Publ. No. 60-20,685. The writing board copying apparatus mentioned above includes a video camera for taking an image of a surface of a writing board and a printer for printing out the video image as a hard copy.
One problem with the writing board copying apparatus described above is that the apparatus is not always located in front of a writing board so as to view directly the center of the writing board. If it is located off-center of the writing board, the writing board copying apparatus views the center of the writing board at an angle. Therefore, the copies image is unavoidably subjected to the effect of perspective, resulting in a distorted image.
Another problem with such writing board copying apparatus is that the apparatus is not always located at the level of the center of the writing board. Therefore, the apparatus is usually inclined upward at an angle so as to view the center of the writing board, resulting in the occurrence of distortion.
On the other hand, there are various kinds of heat sensitive sheets which differ in size, thickness, heat sensitivity and color tone. For adapting the heat sensitive copying apparatus for use with such various kinds of heat sensitive sheets, the apparatus should be changeable as to printing conditions according to characteristics of each hat sensitive sheet used. Such a selection of printing conditions is troublesome and makes it impossible to effect quick printing.